triple head: xrandr commands ignored

Alex Deucher alexdeucher at
Mon May 1 13:23:08 UTC 2017

On Fri, Apr 28, 2017 at 9:55 PM, Michel Dänzer <michel at> wrote:
> On 29/04/17 04:15 AM, Alex Deucher wrote:
>> On Fri, Apr 28, 2017 at 5:46 AM, Felix Miata <mrmazda at> wrote:
>>> Felix Miata composed on 2017-04-28 05:22 (UTC-0400):
>>>> Felix Miata composed on 2017-04-27 06:35 (UTC-0400):
>>>>> openSUSE Tumbleweed
>>>>> kernel 4.10.10
>>>>> server 1.19.3
>>>>> ATI HD5450 PCIe gfxcard (Cedar)
>>> ...
>>> When I use this startup script:
>>> xrandr --output DVI-0 --primary --mode 1920x1200 --left-of HDMI-0
>>> xrandr --output HDMI-0 --mode 1920x1080
>>> xrandr --output VGA-0 --mode 1680x1050 --above DVI-0
>>> xrandr --dpi 108
>>> things improve dramatically. 1920x1080 appears right of 1920x1200, and mouse can
>>> reach them both, but 1680x1050 remains asleep.
>>> Xrandr and Xorg.0.log combined:
>>> Is this low-budget Sapphire ATI Cedar gfxcard not supposed to be able to produce
>>> on all three outputs at once?
>> All evergreen cards only have 2 PLLs so that means they can only
>> support two independent clocks.  If you want to use more than two
>> displays, you'll need to use displayport or for non-displayport, at
>> least two of the displays need to be using the exact same display
>> timing.
> BTW, does only the pixel clock need to be identical, or do the
> vertical/horizontal blanking periods also need to happen at the same time?

Only the clock.  There are enough crtcs for the timing.


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